On 1 September 2010, Lucie Pautet showed up for her first day of work. An empty, light-filled office awaited the new hire at NEPTUNE Canada, in Victoria, B.C., the aboveground headquarters of an underwater ocean observatory.

Ten days later, that sunny space was a distant memory. She was at sea and working the night shift. She'd rise daily at 9 p.m. and walk around the R/V Thomas G. Thompson, an 84-meter-long ship, checking in on the next day's plan for installing instruments and cables on the ocean floor. Then she'd settle in at a workbench in the low-ceilinged control room and watch the footage transmitted by ROPOS, a remotely operated submersible vehicle.

ROPOS went out for almost daily dives that lasted between 10 and 30 hours. Its front camera's saucer-size lens, protruding like an alien eyeball, fed the NEPTUNE crew a high-definition view of the submersible's pincerlike arms. Pautet and her colleagues literally worked in the dark; they spent a month at sea with the lights turned off, staring raptly at a screen at the front of the control room as the submersible explored the water, manipulated tools, and used its graspers to gently position new data-collecting instruments.

"One night we had an amazing moment," Pautet gushes. "We were in a hundred meters of water, and all of a sudden we were surrounded by a school of sunfish." Then she catches herself—there is no "we" down there, only a robot puttering through the water below. "You kind of identify with ROPOS at some point," she says with a quizzical shake of the brown curls framing her face. "Especially when the room is dark and all you have is the screen in front of you, and it's just as if you were in the vehicle, just looking around."

For Pautet and her crewmates, communing with a roving hunk of metal is a fact of life, a reflection of the inseparability of their duties. Adrift on the Juan de Fuca Plate, off the coast of Vancouver Island, the team of scientists and engineers was tending to an unconventional observatory that sprawls some 3000 meters below them on the ocean floor. Cables from the shore provide continuous power and a communications link to five underwater bunkers, called nodes, that connect 160 instruments over the seismically active plate. But to install new instruments, the crew needs ROPOS. To power them and extract their data, the team needs undersea extension cables. And to lay those cables, the scientists again count on ROPOS.

As the lead engineer, Pautet must pull off the last-minute miracles to make it all happen. "Every day, it's like being MacGyver," she says. "There are so many little problems you have to solve with a little tape, by scavenging a can, by thinking on your feet."

The team had set out to lay three thick cables, each between 4 and 8 kilometers long, to connect a new node on the plate's Endeavor Ridge. The ridge is covered with black smokers, tall and spindly hydrothermal vents that jut like chimneys and spout sulfurous, 300° C water from Earth's crust. While they spew, the black smokers easily melt ill-placed instruments, and when the water eventually cools, its minerals form new rock that encrusts whatever it lands on.

Pautet confronted the ocean floor's geologic jungle gym from her perch at a raw wooden desk in the ship's control room. With ROPOS creeping through a few hundred meters of water an hour, Pautet and her teammates surveyed a route for the cable, mapping the mountains and chasms cut into Earth's crust. She sized up whether the cable could withstand the tension imposed by each slope and drop-off, and she hunted for the flattest, cleanest path to the new node. "Between the surveying of the route, the laying of the cable, and the inspection afterward, you're talking about several days of intensive work," she recalls with a weary smile. "It's intense, but you're also accomplishing this amazing technological feat."

For Pautet, this cruise marked a new chapter in a meandering career in which the 40-year-old has trained as an engineer, a globe-trotting, cable-laying technician, and a coastal waters scientist. Now she's all three at once.

Before discovering the ocean, she dreamed of the sky. As a teenager growing up in France, Pautet and a childhood friend imagined themselves becoming rocket scientists and lofting astronauts into low Earth orbit and beyond. They both applied to France's top aerospace school. Her friend got in, but Pautet did not.

She ended up at École Centrale de Lyon, a university with a strong pedigree in acoustics. She immersed herself in a broad engineering curriculum, as is the custom in French education, before concentrating in aeroacoustics—the study of noise made by rockets and airplanes. A year abroad, at Pennsylvania State University, stretched into two years.

While studying for a master's degree in aerospace engineering, she made a routine but fateful trip to the library at Penn State. Scanning the shelves, she came across a textbook on underwater acoustics and began flipping through the pages. "I thought, 'Wow. This is so cool. This is what I want to do,' " she recalls.

On the spot, Pautet shifted her focus. She moved to California to begin a doctoral program in underwater acoustics at the Scripps Institution of Oceanography. There she took up scuba diving—and the ocean came alive for her. "Whenever I go diving, it's like you open a door to another world," she reflects. "It's amazing stress relief. For one hour you're out in space."

After collecting her Ph.D., she took a job at a NATO research center in Italy, where she ran experiments on underwater acoustics along the coast of Elba, in the Mediterranean. The job was idyllic, with fine Italian food and fantastic diving, and access to a research ship whenever she needed one. "It doesn't get better than that!" she recalls.

But eventually, she says, she grew nostalgic for her engineering roots. So she left for the CTBTO Preparatory Commission, in Vienna, where she helped set up networks of seismic sensors that will one day make the comprehensive nuclear test-ban treaty verifiable. Bouncing from ship to ship, she set up monitoring stations on several remote islands around the world.

It was then she mastered the art of undersea cables. She became fluent in the language of underwater terrain, reading the hills and valleys that threatened to abrade her cable. She also learned of the dangers: Should the weather worsen, she and her crew had to know when to cut an unspooling cable, which essentially ties a ship to the ocean floor. Waiting too long could capsize the vessel, risking their lives.

After several voyages, though, Pautet again began to feel dissatisfied—this time with the lack of science. "So when I came across this ocean observatory, I thought, that's exactly what I want," she says. "A year later, here I am."

As the early morning hours ticked by aboard the Thomas G. Thompson, Pautet and her half-dozen night shift companions launched a daily countdown to scrambled eggs. She made a point to slip out on deck each morning to watch the sun climb over the horizon. Later, in the canteen, she could relax and socialize as the rest of the ship stirred to life.

Of all her waterborne wanderings, it's the one month she spent here on Endeavor Ridge that brings a catch to Pautet's voice. "I have never been around something like that—it was breathtaking," she says. "You're so deep, and with the black smokers it's as hostile as it can get. We're installing instruments there, doing things no one has ever done."

Now back on land in her sunny, still-empty office, she eagerly prepares for her next trip out onto the ridge. Easily forgotten are the night shift's long and lonely hours, the few wrenching days of seasickness, and the storms that rocked the ocean, sending the crew flying off their chairs. What remains instead is a single image. As the aerospace expert turned underwater engineer sees it, "It's your step on the moon."